TIME VARIABILITY OF EMISSION LINES FOR FOUR ACTIVE T TAURI STARS. I. OCTOBER–DECEMBER IN 2010 (original) (raw)
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Magnetospheric accretion-ejection processes in the classical T Tauri star AA Tauri
Astronomy and Astrophysics, 2007
Context. Accretion and ejection are complex and related processes that vary on various timescales in young stars. Aims. We intend to investigate the accretion and outflow dynamics and their interaction from observations of the classical T Tauri star AA Tau. Methods. From a long time series of high resolution (R=115,000) HARPS spectra and simultaneous broad-band photometry, we report new evidence for magnetospheric accretion as well as ejection processes in the nearly edge-on classical T Tauri star AA Tau. Results. AA Tau's light curve is modulated with a period of 8.22d. The recurrent luminosity dips are due to the periodic occultation of the central star by the magnetically-warped inner disk edge located at about 9 R ⋆ . Balmer line profiles exhibit a clear rotational modulation of high-velocity redshifted absorption components with a period of 8.22 days as well, with a maximum strength when the main accretion funnel flow passes through the line of sight. At the same time, the luminosity of the system decreases by about 1 mag, indicative of circumstellar absorption of the stellar photosphere by the magnetically-warped, corotating inner disk edge. The photospheric and HeI radial velocities also exhibit periodic variations, and the veiling is modulated by the appearance of the accretion shock at the bottom of the accretion funnel. Diagnostics of hot winds and their temporal behaviour are also presented. Conclusions. The peculiar geometry of the young AA Tau system (nearly edge-on) allows us to uniquely probe the acretion-ejection region close to the star. We find that most spectral and photometric diagnostics vary as expected from models of magneticallychannelled accretion in young stars, with a large scale magnetosphere tilted by 20 • onto the star's spin axis. We also find evidence for time variability of the magnetospheric accretion flow on a timescale of a few rotational periods.
The extreme T Tauri star RW Aur: accretion and outflow variability
Astronomy and Astrophysics, 2005
We present an analysis of the classical T Tauri star RW Aur A, based on 77 echelle spectra obtained at Lick Observatory over a decade of observations. RW Aur, which has a higher than average mass accretion rate among T Tauri stars, exhibits permitted (Hα, Hβ, Ca II, He I, NaD) and forbidden ([OI]6300Å) emission lines with strong variability. The permitted lines display multiple periodicities over the years, often with variable accretion (redshifted) and outflow (blueshifted) absorption components, implying that both processes are active and changing in this system. The broad components of the different emission lines exhibit correlated behavior, indicating a common origin for all of them. We compute simple magnetospheric accretion and disk-wind Hα, Hβ and NaD line profiles for RW Aur. The observed Balmer emission lines do not have magnetospheric accretion line profiles. Our modeling indicates that the wind contribution to these line profiles is very important and must be taken into account. Our results indicate that the Hα, Hβ and NaD observed line profiles of RW Aur are better reproduced by collimated disk-winds starting from a small region near the disk inner radius. Calculations were performed in a region extending out to 100 R . Within this volume, extended winds originating over many stellar radii along the disk are not able to reproduce the three lines simultaneously. Strongly open-angled winds also generate profiles that do not look like the observed ones. We also see evidence that the outflow process is highly dynamic -the low-and high-velocity components of the [OI](6300Å) line vary independently on timescales of days. The apparent disappearance from December 1999 to December 2000 of the [OI](6300Å) low velocity component, which is thought to come from the disk-wind, shows that the the slow wind can exhibit dramatic variability on timescales of months (placing limits on how extended it can be). There is no comprehensive explanation yet for the behavior of RW Aur, which may in part be due to complications that would be introduced if it is actually a close binary.
Monthly Notices of the Royal Astronomical Society, 2011
Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (T e ≃ 80, 000 K) and dense (n e ≃ 10 10 cm −3) component associated with the large scale jet. This hot component is formed very close to the base of the jet providing fundamental information on the jet formation mechanism. In this series, we have investigated whether this component can be formed in disc winds, either cool or warm. To conclude the series, jet launching from the interface between the magnetic rotor (the star) and the disc is studied. Synthetic profiles are calculated from numerical simulations of outflow launching by star-disc interaction. Profiles are calculated for several possible configurations of the stellar field: dipolar (with surface strengths, B * of 1, 2 and 5 kG) or dynamo fed. Also two types of discs, passive or subjected to an αΩ-dynamo, are considered. These profiles have been used to define the locus of the various models in the observational diagram: dispersion versus centroid, for the profiles of the Si III] line. Bulk motions produce an increasing broadening of the profile as the lever arm launching the jet becomes more efficient; predicted profiles are however, sensitive to the disc inclination. Models are compared with observations of the Si III] lines obtained with the Hubble Space Telescope. In addition, it is shown that the non-stationary nature of star-disc winds produce a flickering of the profile during quiescence with variations in the line flux of about 10%. At outburst, accretion signatures appear in the profiles together with an enhancement of the wind, producing the correlation between accretion and outflow as reported from RU Lup, AA Tau and RW Aur observations.
Astronomy & Astrophysics, 2010
Context. Spectral observations of classical T Tauri stars show a wide range of line profiles, many of which reveal signs of matter inflow and outflow. Hα is the most commonly observed line profile owing to its intensity, and it is highly dependent on the characteristics of the surrounding environment of these stars. Aims. Our aim is to analyze how the Hα line profile is affected by the various parameters of our model, which contains both the magnetospheric and disk wind contributions to the Hα flux. Methods. We used a dipolar axisymmetric stellar magnetic field to model the stellar magnetosphere, and a modified Blandford & Payne model was used in our disk wind region. A three-level atom with continuum was used to calculate the required hydrogen level populations. We used the Sobolev approximation and a ray-by-ray method to calculate the integrated line profile. Through an extensive study of the model parameter space, we investigated the contribution of many of the model parameters to the calculated line profiles. Results. Our results show that the Hα line is strongly dependent on the densities and temperatures inside the magnetosphere and the disk wind region. The bulk of the flux comes most of the time from the magnetospheric component for standard classical T Tauri star parameters, but the disk wind contribution becomes more important as the mass accretion rate, the temperatures, and the densities inside the disk wind increase. We also found that most of the disk wind contribution to the Hα line is emitted at the innermost region of the disk wind. Conclusions. Models that take into consideration both inflow and outflow of matter are a necessity to fully understand and describe classical T Tauri stars.
Which jet launching mechanism(s) in T Tauri stars
Astronomy & Astrophysics, 2006
Aims. We examine whether ejection phenomena from accreting T Tauri stars can be described by only one type of self-collimated jet model. Methods. We present analytical kinematic predictions valid soon after the Alfvén surface for all types of steady magnetically self-confined jets. Results. We show that extended disc winds, X-winds, and stellar winds occupy distinct regions in the poloidal speed vs. specific angular momentum plane. Comparisons with current observations of T Tauri jets yield quantitative constraints on the range of launching radii, magnetic lever arms, and specific energy input in disc and stellar winds. Implications on the origin of jet asymmetries and disc magnetic fields are outlined. Conclusions. We argue that ejection phenomena from accreting T Tauri stars most likely include three dynamical components: (1) an outer self-collimated steady disc wind carrying most of the mass-flux in the optical jet (when present), confining (2) a pressure-driven coronal stellar wind and (3) a hot inner flow made of blobs sporadically ejected from the magnetopause. If the stellar magnetic moment is parallel to the disc magnetic field, then the highly variable inner flow resembles a "Reconnection X-wind", that has been proven to efficiently brake down an accreting and contracting young star. If the magnetic moment is anti-parallel, then larger versions of the solar coronal mass ejections are likely to occur. The relative importance of these three components in the observed outflows and the range of radii involved in the disc wind are expected to vary with time, from the stage of embedded source to the optically revealed T Tauri star phase.
Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae
Monthly Notices of the Royal Astronomical Society, 2018
Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the Hα profile were observed during the 2015–2016 period in RY Tau and dur...
Characteristic times of wind variability in classical T Tauri stars
Bulletin of the Crimean Astrophysical Observatory, 2013
Results of observations of short term wind variability in the classical Τ Tauri stars RW Aur and DR Tau are presented. Since the H CaII emission is absorbed by the absorption component of the H⑀ line, which arises in the wind at a radial velocity of about -120 km/s, the ratio of equivalent widths of the H and K emis sion lines of ionized calcium is used as an indicator of the line of sight wind density. Observations showed that the wind densities of RW Aur and DR Tau vary with a characteristic time of 4 to 5 days, i.e., with a period that is somewhat shorter than the period of the axial rotation of these stars. These results are interpreted in the framework of the conical wind model, which predicts cyclic repetitions of accretion and ejection events caused by the interaction of the star's magnetosphere with the ionized gas at the inner boundary of the accre tion disc.
Iron and helium emission lines in classical T Tauri stars
Results are presented for the He emission in 31 CTTS from the Taurus-Auriga molecular cloud spanning two orders of magnitude in the mass accretion rate, and for the Fe emission in DR Tau, based on a series of high resolution echelle spectra. The He lines admit a description in terms of a narrow component ( NC) and a broad component (BC). The NC has FWHM between 32-55 km/s and centroid velocities near zero km/s or moderately redshifted, consistent with an origin in the postshock region of the magnetospheric accretion model. The BC, with FWHM between 128 and 287 km/s and centroid velocities between -93 and +35 km/s, includes a wind and an accretion component; we argue the BC is predominantly formed in the wind. Estimates of the wind and accretion component equivalent widths are oppositely related to the NC, so the NC equivalent width increases with the accretion component but decreases as the wind component increases. The NC is undetectable where profiles appear dominated by the wind,...
Evidence of hot high velocity photoionized plasma falling on actively accreting t tauri stars
2013
The He ii (1640 Å) line and the resonance doublet of N v (UV1) provide a good diagnostic tool to constrain the excitation mechanism of hot (T e > 40,000 K) atmospheric/magnetospheric plasmas in T Tauri stars (TTSs). Making use of the data available in the Hubble Space Telescope archive, this work shows that there are at least two distinct physical components contributing to the radiation in these tracers: the accretion flow sliding on the magnetosphere and the atmosphere. The N v profiles in most sources are symmetric and at rest with respect to the star. The velocity dispersion of the profile increases from non-accreting (σ = 40 km s −1) to accreting (σ = 120 km s −1) TTSs, suggesting that the macroturbulence field in the line formation region decreases as the stars approach the main sequence. Evidence of the N v line being formed in a hot solar-like wind has been found in RW Aur, HN Tau, and AA Tau. The He ii profile has a strong narrow component that dominates the line flux; the dispersion of this component ranges from 20 to 60 km s −1. Current data suggest that both accretion shocks and atmospheric emission might contribute to the line flux. In some sources, the He ii line shows a broad and redward-shifted emission component often accompanied by semiforbidden O iii] emission that has a critical electron density of ∼3.4 × 10 10 cm 3. In spite of their different origins (inferred from the kinematics of the line formation region), N v and He ii fluxes are strongly correlated, with only the possible exception of some of the heaviest accretors.